Ragnarok : the age of fire and gravel

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COULD A COMET STRIKE THE EARTH? 85

“Tn the years 1767 and 1779 Lexell’s comet passed though the midst of Jupiter’s satellites, and became entangled temporarily among them. But not one of the satellites altered its movements to the extent of a hair’sbreadth, or of a tenth of an instant.” *

But it must be remembered that we had no glasses then, and haye none now, that could tell us what were the effects of this visitation upon the surface of Jupiter or its moons. The comet might have covered Jupiter one hundred feet—yes, one hundred miles—thick with gravel and clay, and formed clouds of its seas five miles in thickness, without our knowing anything about it. Even our best telescopes can only perceive on the moon’s surfacewhich is, comparatively speaking, but a few miles distant from us—objects of very great size, while Jupiter is sixteen hundred times farther away from us than the moon. :

But it is known that Lexell’s comet was very much demoralized by Jupiter. It first came within the influence of that planet in 1767 ; it lost its original orbit, and went bobbing around Jupiter until 1779, when it became entangled with Jupiter’s-moons, and then it lost its orbit again, and was whisked off into infinite Space, never more, perhaps, to be seen by human eyes. Is it not reasonable to suppose that an event which thus demoralized the comet may have caused it to cast down a considerable part of its material on the face of Jupiter ?

Encke’s comet revolves around the sun in the short period of twelve hundred and five days, and, strange to say—

“The period of its revolution is constantly diminishing ; so that, if this progressive diminution always follows the same rate, the time when the comet, continually

—— eS Se eee : * “Edinburgh Review,” October, 1874, p. 205.